Electric pulse delay circuit



June 3, 1952 D. H. wEsTwooD 2,599,305

ELECTRIC PULSE DELAY CIRCUIT Filed March 24, 1950 e I Pfr/77a ,M75-@Mpman /an tw 0 5 /7 Z /vauff 45a' /IUA U /g/ /zxf P0455 $5927 am,

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Patented June 3, V1952 ELECTRIG PULSE DELAY CIRCUIT David H; Westwood,-Haddoneld, N; J-., assignor` to'Radio Corporationof America, a corporation Application March 24, 1950;.Serial/Noe151677 claims. (ci. 25o- 215VVV My invention relates to electricaldelay circuits and particularly. to a circuit for producing an electrical` pulse that may be delayed a variable amount.

An object of the invention istoprovideA an `im proved circuit. for producing an electrical pulse of variable delay..-

A. further objectof the invention is to provide an improved pulse delay circuitof the typewhereinthe amount ofv delay determined bythe settingofaelipping level for a .wave of. sawtooth wave form or of some other wave form having a sloping portion. Y

A-still further object. of the inventionr is to provide an improved delay circuit for producing apulse that is delayed by an amount that is continuouslyVA varied.

A still further object of the invention is to providean improveddelay vcircuit for producing a delayy circuit for producing a delayed pulsel that remainsof constant amplitudev as the amount of delay is varied.vv

In practicing ,the present invention two vacuum Y tubeshaving a common cathode resistor are employed. Asawtooth wave of negative polarity is applied. Vto the grid of. the rst tube and. the delayed pulse is taken off vthe anode'of the second tube.

The circuit adjustments are such Vthat during apositive portion of. the applied sawtooth wave A andbefore the negative going portion begins the 'rst tube is conducting and .the second tube is biased, to. cut-off.

When the negative sawtooth wave is applied, the rsttube is driven to cut-off at a time depending upon the bias setting for the rst tube. This results inthe second tube being driven to a conducting condition thereby lowering its anode potentialrto .produce the front edge of the The delayed pulse terminates during the return line` period of the applied sawto'oth; voltage. Whilev the timing of the back edge of the delayed pulse is not of interest in thefexample herein described, the circuit maybe employed 'to utilize the back edge timing.

The invention willbe better understood from the following description taken in connection withthel accompanying drawing. in which:

Figure. 1" is a circuit 'diagram 'of a` preferred embodiment of theinvention, Aand Figure 2 is a group of graphs that are referred Referring toFigure Lasuitable sawtoothlwave generator IU supplies a sawtooth wave suchV as shown by the graph'y I hier. example.4 The sawtooth wave cyclesl are /producedin synchronism with electrical pulses shown-bygraph `I2f^and supplied from a pulse generator I3. inthe specii'lc example illustrated the pulses I22have a repetition rate of 3000 per'se'cond. f-

' The sawtooth'wave generator'y III' maybe any one of severall well known typesand requiresno detailed description. If desired,V the generator I0 may be a triangularv wave generator;` It willl be apparent that theV particular 'shape and-values ofthe wave II are not critical'-anddependupon the design-and application `of'a particular delay circuit.

The specific values indicated'oxr-'the drawing, both las to the wave II', the pulses'- I2-,-andthe circuit constantsy are givenmerelyfor the purpose of illustrating one speciilc example;

Thesawtooth wave I-I is applied with negative polarity through a coupling capacitor- I 4/ 'to' the grid of a vacuum` tube. VI The tube VI-'andf-a tube V2 havel a common'cathode resistor IB.- In the example shown,V the tubes VI and lV21 are each one half of a vacuum tube type 12AX'1.

Anode potential is applied-directly tol theH anode of the tube VI whereby' the tube- VI actsv asa cathode follower. Anode potential is applied to the anode of the ltube V2 through an anode resistor I1.

The delayed outputr pulse '2li is taken off' the anode of tube' V2.

Referring now to the grid biasing'meansfor the two tubes', the tube VI has bias voltageY applied to its grid through a grid resistor I8. This bias voltage Aissupplied from anvariable tap- I9 on one section of a. potentiometer '-2I; This potentiometer is connected acrossthe anode'voltage supply for the. 'tubes "VI' and V2. In the specific example shown,V the potentiometer` 2l consists of three resistor sections. the middle section being adjustable to permit' adjusting.Y the amount of'phase change of the output pulsef20 for a given change in the position of the' variable tap I9.

By varying the position of the tapl Illv 'and thereby varying the bias `on the tube VI',` the timing. of the front edge of the output pulse-20 is varied as will b'e explained hereinafter.

The tube V2 has bias'applied to its' gridby way of a lead`22. The bias is suppliedfroma potentiometer 23 that is connected across the anode supply of 'the' tubesA yVI and IV2'. Inl the specic example illustrated',l the potentiometer 23 consists' of three resistor sections. and the bias is taken'off the'middle section byfa"tap'24f'that',

preferably is adjustable. In the preferred oper-y ation the tap 24 is not moved, after it is once adjusted.

Tap I9 determines the D.C. operating level 0f the applied voltage wave, thus, the voltage on the grid at any particular time is the sum of the D.C. voltage on tap I9 and the instantaneous value of the applied sawtooth wave referred toits average value. As previously stated, during a positive portion of the applied sawtooth wave and before the negative going portion begins, tube VI is conducting and tube V2 is biased to cut-off. It will be noted that the flow of current from VI through cathode resistor I6 makes the cathode of tube V2 positive with respect to its grid and thus biases tube V2 to cut-off. Under this condition the output voltage at the anode of tube V2 is a maximum and is equal to the plus B voltage, which, in this instance, is 300 volts. The tap 24 furnishes the bias to the grid of V2 and hence determines the voltage to which the. cathode vof V2 must be lowered in order to start anode to cathode conduction in V2.

Now consider the circuit action when the negative goingportion of the applied sawtooth wave II begins. Cathode follower action of VI causes the voltage across cathode resistor I6 also to go more negative and finally a point'is reached on the negative slope of II -at which the cathode to grid voltage of V2 is such as to cause anode to cathode conduction in V2. This is indicated by the broken line in Figure 2. As a result of V2 becoming conducting its anode voltage drops thereby producing the front edge of the output pulse 20. When V2 is fully conducting the voltage across the cathode resistor I6 is held to a constant value near that of the grid voltage and determined by the tube characteristics of V2. As the voltage Wave on the grid of VI continues to go more negative the conduction through VI is cut off. Thus the front edge of pulse 2U has been caused to occur at a time delayed, as indicated in Figure 2, by an amount determined both by the shape of the applied voltage wave and the relative value of bias voltages on taps I9 and 24.

Described diierently the circuit action is thus: The bias voltage set by tap 24 determines the voltage necessary on the cathode of V2 to cause conduction in V2 While the bias voltage furnished by the tap I9 determines at which point on the applied wave this particular voltage is caused to occur on the cathode of V2 by the cathode follower action of VI. Therefore, as the tap I9 is varied the point on the applied wave at which V2 conducts is Avaried thus varying the delay of the leading edge of the output pulse.

The pulse 29 remains at a Xed reduced voltage value so long as the tube V2 conducts and the tube VI remains cut-off. As the voltage of sawtooth wave II rises during the return period, a point is reached where tube VI again becomes conducting and the tube V2 is again driven to cut-oft. 'Ihis produces the back edge of the pulse 20. I

It should be noted that as the tap I9 is varied to vary the delay of output pulse 20, there is no change in the amplitude of the pulse 20 since lthe operating characteristics of the tube V2 rey.rnain`unchanged. For some applications of the invention this is very important.

Y of pulse 20.

dle resistor section of the potentiometer 23 should comprise a greater percentage of the total potentiometer resistance than indicated on the drawing.

It will be understood that, if desired, the output pulse 20 may be differentiated to obtain a delayed and comparatively narrow pulse which will occur in response to the occurrence of the front edge Or, if preferred, the front edge of pulse 20 may be used to trigger a multivibrator to produce delayed pulses of the desired width.

It will be apparent that the invention is not limited to the use of sawtooth or triangular waves on the grid vof the tube VI. While a wave form having a linear portion usually is preferred, other wave forms such as a sine wave form may be employed in some instances.

It will be apparent that the timing of the back edge of the output pulse may be utilized particularly if the input wave is a triangular wave or if it is a sawtooth wave, for instance, that has a comparatively steep front slope and a gradual back slope or return. y

The circuit values on the drawing are given merely by Way of example and are in microfarads and thousands of ohms.

What I claim is: v f

1. In combination, means for producing a sawtooth wave having a gradual sloping portion that goes increasingly negative, a pair of Vacuum tubes each having a cathode, a grid and an anode, an

anode voltage supply, the first of said tubes being normally conducting, means forY applying said wave to the grid of the first of saidtubes with sufficient amplitude to drive said nrsttube to anode current cut-off, a cathode resistor common to said cathodes and through which said cathodes are connected to the low voltage end of said anode voltage supply, an anode resistor for the second of said tubes through whichthe high voltage end of said supply'is connected to the anode of said one tube, saidhigh voltage end also being connected to the anode of the other tube, means for taking a rectangular output 'wave oil the anode end of said anode resistor, means for applying a bias Voltage to the grid of one of said tubes, means for varying said bias whereby the starting time of said output wave is varied, where by there is obtained a rectangular wave having a front edge that has a timing determined by the Value of said bias.

2. In combination, means for producing a wave having a negative polarity portion that has substantially a linear slope, a iirst vacuum tube and a second vacuum tube each having a cathode, a grid and an anode', an anode voltage supply, said first tube being normally conducting, means for applying said wave to the grid of said iirst tube with sufcient amplitude to drive said first tube to anode current cut-olf, a cathodev resistor common to said cathodes and through which said cathodes are connected to the low voltage end of said anode voltage supply, an anode resistor for the second of said tubes through which vthe high voltage end of saidsupply is connected to the anode of said one tube, said high voltage end being connected directly Vto .the anode of the other tube, means for taking av rectangular output wave off the anode of said second tube, means for applying a bias' voltage to the grid of said first tube, and means for varying Saidbias whereby the starting time'of said output wave is varied.

3. A circuit for producing delayed pulses, said circuit comprising a pair of vacuum tubes each having a cathode, a control grid andan anode,

said tubes having a common cathode resistor, the first of said tubes having a positive operating voltage applied directly to its anode Whereby it functions as a cathode follower tube, the second of said tubes having an anode resistor through which a positive operating voltage is applied to its anode, an output connection from the anode end of said anode resistor for supplying a delayed output pulse, means for applying bias voltages to the control grids of said tubes such that the rst tube is normally conducting and the second tube is normally biased to cutoff, means for applying to the grid of the first tube a voltage for driving it increasingly negative and sufficiently negative to drive said first tube beyond cut-oil, said bias on at least one of said tubes being variable for varying the delay of said output pulse with respect to the starting time of said voltage that is applied to the grid of the rst tube.

4. A circuit for producing delayed pulses, said circuit comprising a pair of vacuum tubes each having a cathode, a control grid and an anode, said tubes having a common cathode resistor, the rst of said tubes having a positive operating voltage applied directly to its anode whereby it functions as a cathode follower tube, the second of said tubes having an anode resistor through which a positive operating voltage is applied to its anode, an output connection from the anode end of said anode resistor for supplying a delayed output pulse, means for applying bias voltages to the control grids of said tubes such that the first tube is normally conducting and the second tube is normally biased to cut oi, means for applying to the grid of the rst tube a Voltage for periodically driving it increasingly negative and suiciently negative to drive said rst tube beyond cut-off, said bias on said rst tube being variable for varying the delay of said 'output pulse With respect to the starting time of said voltage that is applied to the grid of the first tube.

5. A circuit for producing delayed pulses, said circuit comprising a pair of vacuum tubes each having a cathode, a control grid and an anode, said tubes having a common cathode resistor, the first of said tubes having a positive operating voltage applied directly to its anode whereby it functions as a cathode follower tube, the second of said tubes having an anode resistor through which a positive operating voltage is applied to its anode, an output connection from the anode end of said anode resistor for supplying a delayed output pulse, means for applying bias voltages to the control grids of said tubes such that the first tube is normally conducting and the second tube is normally biased to cutoff, means for applying to the grid of the rst tube a negative sawtooth voltage for periodically driving it increasingly negative and suciently negative to drive said first tube beyond cut-01T, said bias on the iirst of said tubes being variable for varying the delay of said output pulse with respect to the starting time of said voltage that is applied to the grid of the rst tube.

DAVID H. WESTWOOD.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,466,044 Schoenfeld Apr. 5, 1949 2,471,268 Gaines May 24, 1949 

